Radioactive Ion Beam Line In Lanzhou Research Articles

Elastic scattering investigation of radioactive B13 and O13 projectiles on a Pb208 target at intermediate energies

Elastic scattering measurements were performed for the proton drip-line nucleus $^{13}\mathrm{O}$ (with ${S}_{p}=1.512$ MeV) and its partner mirror nucleus $^{13}\mathrm{B}$ (with ${S}_{n}=4.878$ MeV) projectiles on a $^{208}\mathrm{Pb}$ target at intermediate energies, namely ${E}_{\mathrm{lab}}=413$ and 254 MeV, respectively. These secondary radioactive ion beams were produced at the Radioactive Ion Beam Line in Lanzhou (RIBLL), Heavy-Ion Research Facility in Lanzhou (HIRFL). The elastic scattering angular distributions for these projectiles show a typical Fresnel diffraction peak at forward angles. Optical model analyses of the angular distributions, using double-folding and global potentials, were performed and different densities for these projectiles were probed.

The calibration of elastic scattering angular distribution at low energies on HIRFL-RIBLL

The precise calibration of angular distribution of heavy-ion elastic scattering induced by Radioactive Ion Beams (RIBs) at energies around Coulomb barrier on the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL) is presented. The beam profile and the scattering angles on the target are deduced by a measurement with two Multi Wire Proportional Chambers (MWPC), and four sets of detector telescopes (including Double-sided Silicon Strip Detectors (DSSD) placed systematically along the beam line, incorporating with Monte Carlo simulation. The MWPCs were used to determine the beam trajectory before the target, and the energies and the positions of scattered particles on the detectors were measured by the DSSDs. Minor corrections on the beam spot and the detector position are performed by assuming the pure Rutherford scattering at angles which are smaller than the related grazing angle. This method is applied for the elastic scattering of 17F on 89Y target at Elab=59MeV and 50MeV.

A method for the measurement of elastic scattering angular distribution at HIRFL-RIBLL

A method is presented for the measurement of differential cross-sections of heavy ion elastic scattering induced by Radioactive Ion Beams (RIBs) on the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The disadvantages of broad beam profiles and limited intensities of the RIBs were overcome using large area detectors, two Parallel-Plate Avalanche Counters (PPACs), two double-sided silicon strip detector (DSSD) telescopes, incorporated with Monte Carlo simulations. The PPACs were used to determine the direction and position of the beam particles. The DSSD telescopes were used to measure scattered particles. Small corrections for the misalignment of detectors and the data normalization were made by assuming the pure Rutherford scattering at very forward angles. The method is suitable for the measurement of the cross-sections on heavy targets at low and intermediate energies, and it has been successfully applied to measure the angular distribution of elastic scattering of 7Be on Pb target at Elab=17.9MeV/u.

A new low-energy radioactive beam line for nuclear astrophysics studies in China

A gas-target system has been newly developed and installed at a Radioactive Ion Beam Line in Lanzhou (RIBLL), which makes RIBLL capable of delivering intense, low-energy RIBs for nuclear astrophysics studies. A 1.7×104-pps intensity 22Na RI beam has been achieved in a commissioning run. With further improvements, a 105-pps intensity of some RI beams with mass A<30 (close to the line of β-stability) can be expected in the near future. Some detection equipment including Germanium and Silicon arrays (or balls) available (or to be constructed) at IMP are briefly introduced. A new low-energy radioactive beam line in China is now ready for nuclear astrophysics studies.

Projectile fragmentation reactions of40Ar at 57 MeV/nucleon

The projectile fragmentation reactions of ${}^{40}$Ar at 57 MeV/nucleon on ${}^{9}$Be and ${}^{181}$Ta targets have been studied by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The momentum distributions of fragments have been measured and the competition between different mechanisms are observed. The production cross sections have been obtained and compared with the empirical parametrization of fragmentation cross section (EPAX), abrasion-ablation (AA), and heavy-ion phase space exploration (HIPSE) models, and the target dependence of fragment cross sections has also been discussed.

Study of proton resonances in 18Ne via resonant elastic scattering of 17F+p and its astrophysical implication

The proton resonant properties in 18Ne, which determine the reaction rate of the key stellar 14O(α,p)17F reaction, have been studied by using a technique of proton resonant elastic scattering of 17F+p. A 4.22 MeV/nucleon 17F radioactive ion (RI) beam was produced via a projectile-fragmentation reaction, and separated by a Radioactive Ion Beam Line in Lanzhou (RIBLL). By bombarding a thick (CH2) n target, the energy spectra of the recoiled protons were measured by two ΔE-E silicon telescopes at the center-of-mass scattering angles of θ c.m.≈175°±5°, θ c.m.≈152°±8°, respectively. Several proton resonances in 18Ne were observed clearly. A further R-matrix analysis of the experimental data is under way to determine the resonant parameters. The present work reports the preliminary results briefly.

Study of proton resonances in 18Ne via resonant elastic scattering of 17F + p and its astrophysical implication in the stellar reaction of 14O(α, p)17F

The stellar 14O (α, p) 17F reaction is thought to be one of the most important breakout reactions from the Hot CNO cycles into the rp-process in Type I X-ray bursters. In the present work, the properties of proton resonances in 18Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a 17F radioactive-ion (RI) beam and a thick proton target. A 4.22 MeV/nucleon 17F RI beam, which was produced via a projectile-fragmentation reaction and experiencing a series of energy degradation, was separated by a Radioactive Ion Beam Line in Lanzhou (RIBLL) and bombarded a (CH2)n target. Energy spectra of the recoiled protons were measured by two sets of ΔE-E silicon telescope at center-of-mass scattering angles of θ c.m. ≈ 175° ± 5°, θ c.m. ≈ 152° ± 8°, respectively. Several proton resonances in 18Ne were observed, and their resonant parameters have been determined by an R-matrix analysis of the differential cross-sections. A doublet structure around 7.10 MeV has been identified and thought to be one state at 7.05 MeV (2+) and another one at 7.12 MeV (4+). The presently calculated total reaction rates of 14O (α, p) 17F are, at least, a factor of 1.2 ∼ 1.9 larger than the previous ones in a temperature region of 1.7 ∼ 3.0 GK mainly owing to the contribution from the 7.05 MeV (2+) state. This result implies that this breakout reaction may play a more important role than previously expected.

Measurement of the total reaction cross section for the mirror nuclei 12N and 12B

The mirror nuclei 12N and 12B are separated by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at HIRFL from the breakup of 78.6 MeV/u 14N on a Be target. The total reaction cross-sections of 12N at 34.9 MeV/u and 12B at 54.4 MeV/u on a Si target have been measured by using the transmission method. Assuming 12N consists of a 11C core plus one halo proton, the excitation function of 12N and 12B on a Si target and a C target were calculated with the Glauber model. It can fit the experimental data very well. The characteristic halo structure for 12N was found with a large diffusion of the protons density distribution.

Configuration of the valence neutrons of 17B**Supported by National Natural Science Foundation of China (10475098, 10605033, 10221003), Chinese Academy of Sciences (CXTD-J2005-1, KJCX2-SW-N18) and Hundred Talent Project of CAS (0501080BR0)

The reaction cross section of 17B on 12C target at (43.7±2.4) MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (Rrms) was deduced to be (2.92±0.10) fm, while the Rrms of the core and the valence neutron distribution are 2.28 fm and 5.98 fm respectively. Assuming a ``core plus 2n'' structure in 17B, the mixed configuration of (2s1/2) and (1d5/2) of the valence neutrons is studied and the s-wave spectroscopic factor is found to be (80±21)%.

The properties of halo structure for 17B

The total reaction cross section (1724 ± 93 mb) of 17B at the energy of 43.7 A MeV on C target has been measured by using the transmission method at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Assuming 17B consists of a core 15B plus two halo neutrons, the total cross section of 17B on C target was calculated with the zero-range Glauber model, where double Gaussian density distributions and Gaussian plus HO density distributions were used. It can fit the experimental data very well. The characteristic of halo structure for 17B was found with a large diffusion of the neutrons density distribution.

Property measurement of the CsI(Tl) crystal prepared at IMP**Supported by Knowledge Innovation Project of Chinese Academy of Sciences (CKJCX2-SW-N18, CKJCX2-SW-N04)

Large-sized CsI(Tl) single crystals, ∼ ϕ100 mm × 350 mm, have been grown successfully, and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou) to measure the energy of heavy ions as a stopping detector. The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared, including the temperature dependence of scintillating light yield.

Experimental study for neutron-rich exotic nuclei 17B

The total reaction cross section of 17B on C target has been measured by using the transmission method at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Assuming 17B consisting of a core 15B plus two halo neutrons, the total cross section of 17B on C target was calculated with the zero-range Glauber model where Gaussian plus HO density distributions were used. It fitted the experimental data very well. A large diffusion was found about the density distribution of 17B. Based on the analysis, the two neutrons halo of 17B was confirmed.

Measurements of the interaction cross-sections for 14Be and 14,15B as projectiles with a new scheme at RIBLL

We have measured the interaction cross-sections (σI) for light neutron-rich nuclei (14Be, 14,15B) at ∼50A MeV at the Radioactive Ion Beam Line in Lanzhou (RIBLL) in IMP with a new scheme. In this scheme, a carbon reaction target was installed at the intermediate focusing point at RIBLL. This scheme allowed us to identify particles before and after the reaction target unambiguously. However, this scheme might suffer a large loss of transmission efficiency in the second half of RIBLL. We checked this effect by changing the emittance of the RI beams. The results showed that a correction of the transmission efficiency is needed to deduce σI. We performed a Monte Carlo type simulation and tried to deduce σI for the above nuclei. Finally, we obtained reasonable σI although their error bars were fairly large. The results were compared with calculations by an energy-dependent semi-empirical formula.

Measurement of reaction cross section for proton-rich nuclei ( A

Radioactive ion beams were produced through the projectile fragmentation induced by 69 MeV/ nucleon 36Ar primary beam on a 9Be target. Measurements of reaction cross sections ( σ R 's) for 44 nuclei with A<30 (mostly proton-rich), on carbon were performed on RIBLL (Radioactive Ion Beam Line in Lanzhou) of HIRFL (Heavy Ion Research Facility in Lanzhou) at intermediate energies around 30 MeV/nucleon by a transmission method. The experimental σ R values for 23Al and 27P are abnormally large compared with their neighboring nuclei. Together with the previous experimental facts such as the binding energy and ground state data, it suggests anomalously large matter root-mean-square radii and proton halo structure in 23Al and in 27P. There is an enhancement for the σ R of 17F + 12C compared with the neighboring isotopes. Considering that the ground state of 17F is 1 d 5/2, this can indicate that there is a proton skin in 17F. The calculation of relativistic density-dependent Hartree model (RDDH) shows that the nuclei 23Al and 27P may have proton-halo structure and 17F may have proton-skin structure. The significance of these measurements is discussed.

Radioactive ion beam line in Lanzhou

Radioactive ion beam line in Lanzhou (RIBLL) has been constructed for the production of short-lived radioactive nuclei and studies of exotic nuclei far from the β-stability line. It has been put into operation recently at the National Laboratory of Heavy Ion Accelerator Lanzhou. RIBLL consists of two doubly achromatic parts with a solid acceptance ΔΩ⩾6.5 msr, momentum acceptance Δp/p=±5% and maximum magnetic rigidityBp max=4.2 Tm. The second part of RIBLL serving as a spectrometer gives an element resolutionZ/ΔZ>150 and mass resolutionA/ΔA>300. The polarized secondary beams can be obtained by using a swinger dipole magnet to change the incident direction of primary projectile from 0° to 5°. The shortest lift time for secondary beams on RIBLL is less than 1 μs. First experiments were performed with neutron rich nuclei for understanding the properties of halo nuclei and exotic nuclear reactions.

Separation and Identification of Isotopes Produced from 20Ne+Be Reaction by Radioactive Ion Beam Line in Lanzhou

The separation and identification of isotopes emitted from the projectile fragmentation reaction of 80 MeV/u 20Ne on 9Be target were carried out by using the radioactive ion beam line in Lanzhou (RIBLL). Many proton rich isotopes are obtained. Their intensity and purity fit the theoretical calculations. Good separation and identification abilities of RIBLL A/ΔA > 300 and Q/ΔQ > 150, are obtained.